1. Field of the Invention
This invention relates to methods and apparatuses for analyzing copper plating solutions, and more specifically to methods and apparatuses for determining concentration of various components in copper plating solutions.
2. Background of the Invention
The determination of organic additives in copper plating baths is based on measuring the effect of the additives on the copper plating potential. U.S. Pat. No. 6,280,602 issued Aug. 28, 2001 for “Method and Apparatus for Determination of Additives in Metal Plating Baths” discloses the methods and apparatuses for electropotential analysis of copper plating solutions, which is incorporated herein by reference in its entirety for all purposes.
Specifically, calibration solutions are used to quantify the correlation between the electroplating potential of the copper plating solution and the additive concentrations therein. The electropotential analysis therefore relies on constant background matrix—especially copper concentration—during all phases of the determination. Some additives have a very large effect on the plating potential. In this case, only a small quantity of the sample is used for analysis, by diluting it with a standard VMS solution having known and constant copper composition. Matrix variation in such diluted sample with respect to copper concentration is negligible, because the dilution with standard VMS results in a copper concentration that is approximately the same as that of the standard VMS.
On the other hand, analysis of those additives that have less significant effect on the plating potential demands use of a much larger sample with less dilution, resulting in more matrix variation, especially with respect to copper concentration, which will inevitably affect the accuracy of the measurement results.
Therefore, an object of the present invention is to reduce the copper concentration variation in the copper plating solutions to be measured, so as to minimize the matrix effect in the organic additive concentration determination.
Moreover, changes in the acidity of the copper plating samples (due to variation in the sulfuric acid concentration therein) can cause measurement errors during the organic additive analysis, since the differences in the sulfuric acid concentration between the calibration solutions and the sample solution result in different electroplating potentials.
Therefore, it is another object of the present invention to provide a method for reducing the variation in the sulfuric acid concentrations in the calibration solutions and the sample copper plating solution to be measured.
Further, the current copper plating solution analysis techniques use ethylenediaminetetraacetic acid (EDTA) as a chelating agent for stabilizing the copper ions in the solution. However, EDTA is a well-known chelating agent that binds almost every component in the periodic table. Therefore, the use of EDTA may have adverse results, such as adsorption and clogging of the analytical tools, or none-specific binding to metal ions other than copper ions and giving false analytical signals.
It is therefore a further object of the present invention to provide a copper-specific chelating agent that does not have the above-described disadvantages of EDTA.
Other objects and advantages will be more fully apparent from the ensuing disclosure and appended claims.